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Plastisphere-driven pollutant enrichment and harmful bacteria proliferation: Emerging ecological risks to Danjiangkou reservoir's water security
Summary
Researchers sampled plastispheres at seven tributary estuaries of China's Danjiangkou Reservoir across wet and dry seasons, finding that plastic surfaces concentrate nitrogen, ammonium, and lead well above ambient water levels while selectively enriching harmful microbes including cyanobacteria and pathogens, with seasonal shifts in community composition and elevated functional gene expression for nitrogen cycling and carbon metabolism.
Plastispheres host unique microbial communities linked to biogeochemical cycling and ecological risks, yet their responses to pollutant enrichment and seasonal dynamics in the Danjiangkou (DJK) Reservoir, China's core South-to-North Water Diversion water source, are poorly understood. We sampled plastispheres and ambient water at seven DJK tributary estuaries (August 2024/wet, January 2025/dry), characterizing pollutant enrichment, microbial assembly (16S rRNA sequencing), functional gene expression (qPCR), and harmful microbial enrichment, with quantitative microbial risk assessment (QMRA). Results demonstrated that the plastisphere serves as a critical sink for aquatic pollutants, leachate from the plastisphere contains 181.20 ± 27.35%, 875.98 ± 77.61%, and 286.21 ± 32.47% higher concentrations of total nitrogen (TN), ammonium (NH₄), and lead, respectively, than ambient water, and no significant seasonal variation in plastic adsorption capacity. Plastisphere microbes had higher alpha diversity (Chao1: +172.41%; Shannon: +28.07%) and network stability, with Proteobacteria (e.g., Pseudomonas) enriched in summer and Flavobacteria dominating winter plastispheres. Functional genes linked to nitrogen cycling (nitrogen fixation: nifH; denitrification: nirS, nirK) and carbon metabolism (rTCA cycle: aclA, pflD; methane formation: mtaABC, mtbA, cdhCDE) were significantly upregulated in the plastisphere, with total RPKM values 30.49 ± 18.64% higher than in ambient water (p<0.05), with water temperature and DO as primary drivers. Notably, plastics selectively enriched harmful microbes, cyanobacterial taxon SIO2C1_sp010672925 (18.80 ± 5.14%) dominated winter plastispheres, and 524 pathogenic OTUs (e.g., Deinococcus_B, 6.70 ± 3.88%) were more abundant on plastispheres, posing non-negligible risks of algal blooms and pathogen dissemination. Our findings reveal that plastics mediate pollutant accumulation, microbial assembly, and functional gene enrichment in tributary estuaries, with seasonal dynamics shaping harmful bacteria proliferation. This study provides critical insights into the ecological impacts driven by plastic pollution in key freshwater reservoirs, supporting targeted water quality management and ecological risk mitigation.